This invention relates generally to ultrasound transducers, and more particularly, to acoustical stacks that are within the ultrasound transducers.
Ultrasound transducers (also commonly referred to as probes) typically have many acoustical stacks arranged in one dimension or in two-dimensional (2D) arrays. Each acoustical stack corresponds to an element within the transducer, and a transducer may have many acoustical stacks therein, such as several thousand arranged in the 2D array.
In an array transducer, the electrical impedance of a transducer element is higher than the input electrical impedance of the ultrasonic imaging system. This higher impedance results in low efficiency of electrical energy transfer between the transducer and the system, leading to a lowered sensitivity and degraded transducer performance. The electrical impedance of the transducer element increases as the size of the element decreases, therefore, 2D arrays experience a greater degree of decreased sensitivity as the size of the elements is smaller compared to elements in 1D arrays.
Attempts have been made to better match the impedance of the system, such as by using poled piezoelectric materials having a high dielectric constant. Additionally, a multi-poled piezoelectric material layer with a complex electrode design and D-matching layers structure has been used. However, complex electrical connections are needed, increasing the overall complexity, especially for 2D arrays.
Therefore, a need exists for reducing the electrical impedance associated with transducer elements within an ultrasound transducer to improve the sensitivity of the ultrasound system.